I went on a bit of a fact finding mission the other day.
Greater Anglia operate Cambridge station so presumably, the OP bought the ticket from a Greater Anglia TVM. Greater Anglia, being a successor of a National Express TOC (WAGN) make use of S&B machines. These machines have had a software revamp quite recently to make them easier to use.
Presumably, the OP saw "London Terminals" on the quick options screen. Under this it would have further displayed "GRT ANG TRNSONLY" or "ANY PERMITTED." After selecting the ticket, a screen showing exactly which ticket had been chose would have appeared, before allowing the customer to purchase a ticket. Among other things, the route would have also been shown. It is not possible to buy a ticket from one of those TVMs without that screen showing up.
Whilst many people within this thread claim that "GRT ANG TRNSONLY" is cryptic beyond the point of coherence, I don't think it takes the brains of Britain to work out what it means. However, I accept that some people may genuinely not be able to decipher it. For the OP, the option of going to the ticket office and speaking to a member of staff was available, but the conscious decision was taken not to do this for reasons only known to the OP. Common sense would dictate that anyone unfamiliar with a system would seek assistance from a member of staff. As I said, I would
never run into a station in a foreign country, use a ticket machine without understanding exactly what I had been sold, then running onto the first train that appeared to be going in the right direction. Consequently, I refuse to accept that someone else would do that. The type of person that would do this is the type of person who is only ever going to learn the hard way.
Some of the defenses offered by well intending(?) members in this thread are akin to a drowning man clutching at straws and really have no place in a thread where someone is asking for help. Whilst I think that in some cases, FCC are unduly harsh (
never more so than in this case where no money was lost,) they have to be given their due for their drive to ensure that all passengers are paying appropriate fares. I make the effort to do so whenever I travel, so everyone else should too.
In terms of outcomes, I don't consider court action or an out of court settlement as a roaring success. The only thing that can be claimed to be a success would be the refunding of the unused outward portion of the ticket held and a charge for the correct ticket. However, given that it was highly unlikely that the OP didn't know what they were doing (unless there's something very seriously wrong) then the out of court settlement should be the pursued option.